Implantable cardiac stimulation device and method that stabilizes ventricular rate during episodes of atrial fibrillation

Abstract

An implantable cardiac stimulation device provides electrical stimulation therapy to stabilize the ventricular rate of a heart during episodes of atrial fibrillation. The stimulation therapy may be a plurality of sub-threshold stimulation pulses delivered to capture AV node vagal innervations following the detection of atrial fibrillation.

What is claimed is: 
     
       1. An implantable cardiac stimulation device comprising:
 an atrial fibrillation detector that detects atrial fibrillation of a heart; and 
 a pulse generator that, responsive to the atrial fibrillation detector detecting atrial fibrillation of the heart, delivers a plurality of stimulation pulses near an AV node of the heart to capture vagal innervations to the AV node during a time period having a duration related to a desired ventricular rate of the heart, the plurality of stimulation pulses configured to capture the vagal innervations to the AV node and to extend a refractory period at the AV node to stabilize a ventricular rate during the atrial fibrillation; 
 wherein the plurality of stimulation pulses delivered near the AV node are set to an energy and/or frequency to avoid capture of the heart; 
 wherein the duration (in ms) is calculated by 
 
       
         
           
             
               
                 
                   
                     60 
                     , 
                     000 
                   
                   Vrate 
                 
                 - 
                 k 
               
               , 
             
           
         
       
       where 80<k<200 and Vrate is the desired ventricular rate. 
     
     
       2. The device of  claim 1 , further comprising a sensing circuit that senses ventricular activity of the heart to monitor ventricular rate. 
     
     
       3. The device of  claim 1 , wherein the pulse generator is arranged to provide the stimulation pulses during successive time periods, each having a duration related to a desired ventricular rate of the heart, and wherein immediately successive time periods are separated by time intervals sufficient to permit a single atrial event to be issued by the heart. 
     
     
       4. The device of  claim 1 , further comprising a sensing circuit that senses ventricular activity of the heart to monitor ventricular rate. 
     
     
       5. The device of  claim 1 , wherein the plurality of stimulation pulses are sub-threshold so that the heart is not captured by the plurality of stimulation pulses. 
     
     
       6. The device of  claim 1 , wherein the plurality of stimulation pulses are set to an energy below an atrial capture threshold of the heart. 
     
     
       7. The device of  claim 1 , wherein the plurality of stimulation pulses are set to an energy level that captures vagal innervations to the AV node, but is below the atrial capture threshold. 
     
     
       8. The device of  claim 1 , wherein the plurality of stimulation pulses have a frequency timed to be delivered during and extend an AV nodal refractory period, such that at least a portion of the plurality of stimulation pulses are set to an energy above an atrial capture threshold of the heart.